To the Editor.—In a letter by Marcia Wakefield and W. James Alexander, MD (1981;246:1900), regarding rubella immunization of susceptible medical students, the method by which rubella immunity was detected was incorrectly identified as the hemagglutination inhibition test. The footnote to this letter correctly identifies the methodology as a rubella-passive hemagglutination system (Rubacell).I mention the discrepancy because in the hospital screening programs that the authors support and urge on the medical community, the Rubacell system provides an extremely quick and easy screening alternative to the older, time-consuming hemagglutination test.It is our sincere hope that with the simplified passive hemagglutination method available, participation in rubella immunization programs among health care professionals can be even more vigorously pursued by the laboratory and infection control professionals in hospitals.